The present invention relates to an influenza vaccine.
More particularly the present invention relates to an inactivated whole virus influenza vaccine and to a method for the preparation thereof.
Influenza virus infection still continues to be an annual threat all over the world. The infection may be asymptomatic or may range from a mild upper respiratory infection to a severe disease complicated by pneumonia that may result in mortality. Although severe disease is more frequent in the very young, the chronically ill and the aged, the economic burden of the disease, even when mild, is enormous in the total number of working days lost.
The preferred strategy to control the disease is still annual routine immunization. For over twenty years it has been recommended that killed influenza vaccine be given annually to all persons with high risk conditions. The guiding principle behind the recommendation has been to reduce the mortality of epidemic influenza, morbidity and to prevent complications.
Inactivated virus vaccines are still today the primary tool used for inoculation against influenza.
Vaccines which are at present employed are whole virion inactivated vaccines wherein inactivation has been effected by using formalin or .beta.-propiolactone (BPL). Also subunit or split vaccines are used for intramuscular (i.m) or subcutaneous (s.c.) immunization.
Live attenuated (i.e. temperature sensitive mutants) are suggested for intranasal (i.n.) application by instillation, aerosol or spray. Most of these vaccines, however, are still only experimental.
The routinely used vaccines purified on sucrose gradient by continuous flow centrifugation, are mostly inactivated by formol, and are whole virions, split or subunit (the latter being aimed especially for children), administered i.m. or s.c. by injection. The efficacy of the vaccines are mostly assessed by seroconversion or by x4 fold rise of humoral antibodies, mainly the hemagglutination inhibition antibodies.
The hemagglutinin of influenza virus is the major surface glycoprotein against which neutralizing antibodies are elicited, however, the isolated glycoproteins obtained by various methods (subunits, genetic engineered or synthetic) is antigenically inferior to whole virus, in producing humoral antibody response and an adjuvant might therefore be required. Moreover, the isolated antigen is not suitable for cases where IgA is the major protective antibody, as is the case in the respiratory tract.
In respiratory tract infections, antibodies of the secretory IgA type have a major role in the defence vs. infection as it neutralizes the virus at its entrance site.
The inactivated vaccines (whole or subunit) are incapable of inducing local antibody production at all or only in negligible level. At the most, a subunit vaccine of the virus can trigger a secondary response and only when it follows a first dose of active virus and not inactive, or subunit. Satisfactory local immunization is therefore not yet available as it is mostly attributed to the presence of live antigen and adequate and safe live vaccines are not yet available.
Beside humoral antibodies, cellular immune response (CMI) is also elicited. In that respect whole virus vaccines are also important. Recently more and more data has been gathered about the importance of CMI in the protection against infection with influenza virus. Cellular immunity is important in that it exhibits cross reactivity among the different strains within the A group, in contrast to the strain specificity of the antibody response. This phenomenon is dependent on the presence of several viral proteins such as the matrix and nucleoprotein. These proteins were conserved during decades as compared to the annual changes in the surface glycoproteins (hemmagglutinin and neuraminadase), which are mainly responsible for the antibody production.
There is great controversy over the safety and efficacy of the current killed vaccine. The use of BPL which was used in the past for inactivation is now prohibited due to its carcinogenicity. Formalin which is still widely used, is responsible for part of the side effects, and recently some doubts as to its safety were raised.